Schistosomiasis remains the most prevalent trematode infection of humans afflicting over 200 million people. There is no vaccine and praziquantel is the only broad-spectrum antischistosomal drug available. The best long- term defense against the appearance and propagation of drug-resistant parasites is continued basic research directed toward understanding the biology of schistosomes as it relates to the identification of novel biochemical and cellular targets for rational drug design. Most cells of adult Schistosoma mansoni are quiescent. The principal exceptions are the reproductive organs, especially the female vitelline glands. Despite of the importance of egg production in pathogenesis and transmission of schistosomiasis, little is known about schistosome cell proliferation. Understanding the role of nuclear proteins in this process could point to alternative approaches for controlling the infection by interfering with parasite development and reproduction. This proposal focuses on one such protein, SMAK (schistosome homologue of the yeast nuclear protein MAK16), as a prototype. Not only do SMAK and MAK16 share significant amino acid sequence similarity, but SMAK can also complement the makl6-1 mutation in yeast. This proposal is designed to investigate the biochemical function of SMAK and to begin to explore its regulation. There are four specific aims: l) To delineate the tissue, cell and subcellular distribution of SMAK in adult S.mansoni using immunocytochemical techniques and specific anti-SMAK antibodies; 2) To determine whether SMAK expression is develop mentally regulated by measuring the level of SMAK messenger RNA in various schistosome stages; 3) To identify proteins that interact with SMAK using a yeast two-hybrid screen to distinguish between a role in cell cycle progression and 60S ribosome subunit biogenesis: 4) To characterize protein sequence motifs that are hypothesized to be involved in the biochemical function and/or regulation of SMAK. These include: a) a novel zinc binding domain: b) two putative nuclear localization sequences: and c) consensus sequences for phosphorylation of SMAK by protein kinase CK2.